BR112021010318A2 - Method for producing holocellulose fibers, use of said fibers, method for producing a strength agent for paper, process for producing paper, paper, use thereof - Google Patents

Abstract

METHOD TO PRODUCE FIBERS OF HOLOCELLULOSIS, USE OF THESE FIBERS, METHOD TO PRODUCE AN AGENT RESISTANCE FOR PAPER, PROCESS FOR THE PRODUCTION OF PAPER, PAPER, USE THEREOF. the present invention relates to a method for producing holocellulose fibers by treat wood-based raw material with an organic peroxide, in which the method comprises loading the organic peroxide continuously into the wood-based raw material during treatment and/or loading the organic peroxide in the wood-based raw material in at least two separate steps with an intermediate alkaline treatment step. Additionally, a process for the production of paper comprising the steps of preparing a papermaking pulp comprising an aqueous pulp slurry comprising cellulosic fibers and having a fiber consistency of 0.1 to 40% by weight, where cellulosic fibers comprise or consist of holocellulose fibers and wherein the amount of wood-based holocellulose fibers is from 0.5 to 100% by weight, based on the total weight of the pulp; supplying the paste on a wire and forming a web; web dewatering; and drying the web, is claimed. The method provides an affordable way to produce holocellulose fibers usable in the process to provide paper with high strength, while effective dewatering can be achieved during the manufacturing process.

Description

METHOD TO PRODUCE HOLOCELLULOSE FIBERS, USE OF SUCH FIBERS, METHOD TO PRODUCE A STRENGTH AGENT FOR PAPER, PROCESS FOR THE PRODUCTION OF PAPER, PAPER, USE THEREOF TECHNICAL FIELD

[001] The present invention relates to a method for producing holocellulose, a method for producing a paper strength agent, a process for producing paper, the paper produced by the process and the uses of the paper produced as defined in the appended claims. .

TECHNICAL BACKGROUND

[002] Wood mainly comprises cellulose, hemicellulose and lignin. The word holocellulose is used to describe a material of lignocellulosic origin that contains hemicelluloses and celluloses after removal of lignin and extractives.

[003] Paper, tissue paper and packaging materials based on wood fibers have historically been used, for example, for printing, hygiene and packaging purposes. Paper as a packaging material has been used to provide mechanical and/or chemical protection for packaged products. There is a growing demand to produce paper more resource-efficiently with, for example, reduced use of fiber feedstock, chemical additives and energy and with efficient production processes. There is also an increasing demand for lightweight paper materials with good mechanical strength, for example to ensure sufficient protection of packaged products. Additionally, there is a desire to reduce the transport required for paper production and therefore it is desirable to use locally available raw materials. Additionally, there is a desire to use raw materials that are ecological and that are not primarily intended for global food production.

[004] Known methods to decrease the amount of fiber raw material while maintaining the strength of the paper involved, for example, the use of different additives to increase the strength of the paper. However, strength additives can have a negative impact on drainage during the papermaking process, which means that it can be more difficult to drain a fiber web on a paper machine. The difficulty of drainage in the papermaking process can result in a decrease in production capacity and higher energy demand, which is highly undesirable. For example, insufficient drainage can lead to lower dry matter content in the dry section of a paper machine, and drying the paper web will require a large amount of energy. Additionally, additives can substantially increase the density of the paper.

[005] There have been previous attempts to improve the strength of paper on a laboratory scale by the use of holocellulose, as described in YANG, X. et al. “Preserving Cellulose structure: Delignified Wood Fibers for Paper Structures of High Strength and Transparency” In Biomacromolecules, May 2018, Vol. 19, No. 7, pp. 3020-3029, ISSN 1525-7797. However, there is still a need to improve the energy efficiency of papermaking processes to produce high strength, low dewatering resistance and low density paper. Additionally, there is a need for an affordable way to produce holocellulose fibers to transpose this concept to industry.

SUMMARY

[006] It is an object of the present invention to minimize the problems identified in connection with the production of state-of-the-art holocellulose fibers. Additionally, it is an objective to minimize the problems identified in connection with the production of state-of-the-art high strength paper materials. Especially, it is an objective to provide an affordable way to produce holocellulose fibers useful in a papermaking process and to provide a process for papermaking which provides paper with improved strength while effective dewatering can be achieved during the papermaking process. manufacturing.

[007] It is also an object of the present invention to provide a paper, for example a paperboard product, having improved strength properties while the density of the paper is at least maintained at an earlier, i.e. not substantially increased, level.

[008] It is also an object of the present invention to provide a papermaking process with improved dewatering. This is also beneficial for press efficiency and can result in a higher dry matter content after the press section of a paper machine. In this way, the need for drying energy in the drying process during papermaking can be reduced.

[009] Accordingly, the present disclosure relates to a method for producing holocellulose fibers usable in a papermaking process by treating the wood-based raw material with an organic peroxide. The organic peroxide may be peracetic acid. The method comprises: i. continuously loading the organic peroxide into the wood-based raw material during treatment; and/or ii. loading the organic peroxide to the wood-based feedstock in at least two separate steps with an intermediate alkaline treatment step.

[010] It was surprisingly noticed that by loading the organic peroxide continuously during treatment instead of loading all the organic acid in a batch at the beginning of a reaction or loading the organic peroxide in at least two steps with an alkaline step in between, the The amount of organic peroxide added during production of the holocellulose fibers can be reduced. Especially in the method involving continuous loading of organic peroxide, it can be ensured that the organic acid reacts mainly with the wood and not with itself. Thus, the total amount of organic peroxide used for the production of holocellulose fibers can be reduced. Thereby, an affordable way of producing holocellulose fibers is obtained.

[011] The method may comprise a step of loading the organic peroxide continuously into the wood-based raw material or in a medium comprising the wood-based raw material. By continuously loading the peracetic acid, a way is obtained to obtain a given concentration of peracetic acid in the reactor. Continuous addition can be done on demand to the reactor by adding a source of a concentrated organic peroxide, suitably peracetic acid.

[012] Alternatively or additionally, the method may comprise two separate organic peroxide treatment steps with an intermediate alkaline treatment step. In the first step, the amount of organic peroxide is adapted so that the reaction to produce holocellulose is started, but the reaction is not completed. In the second step, the amount of organic acid is adapted so that a desired delignification or whiteness level is achieved. The intermediate alkaline step improves the efficiency of the organic peroxide during delignification through the removal of part of the dissolved lignin and through the solubility in alkaline conditions of the partially oxidized lignin. The removal of these two lignin fractions leads to a decrease in the need for peracetic acid to obtain a certain degree of lignin removal. The intermediate alkaline treatment step may be carried out at a pH of 8 or more, suitably from pH 10 to 12, at a temperature of 15 to 100°C at atmospheric pressure and for a duration of at least 1 hour. Washes can be added between these steps. In at least one of the at least two separate organic peroxide treatment steps, the organic peroxide may be loaded in batches or continuously into the wood-based raw material during the treatment. Thus, the loading of organic peroxide can be flexibly chosen.

[013] By the method, holocellulose fibers can be produced in an affordable way, since the use of organic peroxide, e.g. peracetic acid (PAA), can be reduced compared to what has been revealed in the state of the art. .

[014] In either method i) or ii), the treatment with organic peroxide can be carried out at a temperature of 15 to 100°C, suitably from 40 to 90°C. In this temperature range, the amount of organic peroxide required for the production of holocellulose fibers can be kept low. However, the lower the temperature, the longer the reaction time. A reaction carried out at a temperature of 55 to 75°C may be preferable as the amount of organic peroxide required for the reaction can be kept at a low level while the reaction time is still relatively short. In either embodiment i) or ii) of the method, the organic peroxide treatment may be carried out at a pH of 3.8 to 5 or 4.0 to 4.8.

[015] Additionally, continuous charging can be performed at one or more charging rates throughout the treatment. Thus, the charge rate can be easily adapted to the prevailing process conditions.

[016] The present disclosure also relates to a method for producing a paper strength agent useful in a process for producing paper comprising producing holocellulose fibers according to the method described above, optionally microfibrillating the holocellulose fibers to provide holocellulose nanofibrils (CNF), dry the holocellulose fibers or the holocellulose nanofibrils, and break up the dried holocellulose fibers or the holocellulose nanofibrils. In this way, a paper strength agent for use as an additive and based on the wood-based raw material can be provided.

[017] The present disclosure also relates to a process for the production of paper comprising the steps of: a. preparing a papermaking pulp comprising an aqueous pulp slurry comprising cellulosic fibers and having a fiber consistency of from 0.1 to 40% by weight, wherein the cellulosic fibers comprise or consist of wood-based holocellulose fibers and in that the amount of wood-based holocellulose fibers is from 0.5 to 100% by weight, based on the dry weight of the cellulosic fibers, b. supply the paste to a yarn and form a web; ç. drain the web; d. dry from the web.

[018] Paper properties obtained with holocellulose fibers exhibit a large increase in strength properties, eg tensile, compression, out-of-plane, stiffness and with limited or no impact on drainage. Thus, by using wood-based holocellulose fibers in the papermaking pulp, paper with improved strength can be obtained while in the papermaking process effective dewatering is still possible. Additionally, the wood-based raw material for holocellulose fibers is environmentally friendly and not primarily intended for global food production.

[019] Wood-based holocellulose fibers can be produced by treating a wood-based raw material with an organic peroxide. The organic peroxide may be peracetic acid (PAA). Peracetic acid has the advantage of being selective, but it does not oxidize many of the carbohydrates.

[020] Preferably, the holocellulose fibers can be produced by the method described above. In this way, a more affordable way of supplying holocellulose fibers is obtained.

[021] The wood-based raw material used for the holocellulose fibers may comprise hardwood and/or softwood material. Hardwood and softwood are readily available in the Northern Hemisphere and if production is also in the Northern Hemisphere, long transport for the raw material can be avoided. Also, as mentioned above, hardwood and softwood materials do not compete with global food production in the same way as other plant-based raw materials such as corn-based materials, which is a big advantage. The wood-based raw material may consist of hardwood and/or softwood material.

[022] It was surprisingly noted that when holocellulose fibers are added after a refinement step in step a) of pulp preparation, additionally improved strength properties can be obtained. Without being bound by any theory, this may be due to the retention of fiber structure, degree of cellulose crystallinity, hemicellulose content and its structure, where strength properties are positively affected.

[023] Step a) of preparing the papermaking pulp may comprise a step of adding an additive to an aqueous slurry and beating and/or refining the aqueous slurry. Thus, readily available production equipment can be used for the present process. The additive may comprise holocellulose fibers, which may be added in an amount of from 0.5 to 80% by weight or from 2 to 60% by weight or from 4 to 55% by weight, based on the total weight of the fibers. cellulosic In this way, the production process will be economical while the strength of the paper can be improved without impairing the dewatering characteristics. The additive may comprise a dry strength agent chosen from nanocellulosic materials, loaded and unloaded starch, gum derivatives, synthetic copolymers with acrylamide and combinations thereof. Dry strength additives can further improve the strength of the paper. It was noted that cationic starch provides a synergistic effect on paper strength along with holocellulose fibers. Therefore, the additive preferably comprises cationic starch. The cationic starch can be added, for example, in an amount of less than 10% by weight, for example, from 0.5 to 5% by weight, or from 0.8 to 3% by weight, based on the dry weight of the folder.

[024] In one variant, the additive may comprise a holocellulose CNF, i.e. cellulose nanofibrils produced from holocellulose fibers. In this way, additional improved strength properties can be obtained while dewatering is not impaired to the same extent as with current CNF alternatives. The holocellulose CNF can be added in an amount of 0.1 to 10% by weight, or 0.5 to 5% by weight, based on the dry weight of the pulp.

[025] Additionally or alternatively, the additive may comprise a wet strength agent, which may be a resin chosen from urea-formaldehyde resins, melamine-formaldehyde resins, polyamide-amine-epichlorohydrin resins and combinations of the same. The wet strength agent can be used to further increase the dry strength of the fibers.

[026] Alternatively or additionally, the additive may comprise a retention aid chosen from charged or uncharged polyacrylamide (PAM), polyethyleneimine (PEI), colloidal silica bentonite (CS) and combinations thereof. The retention aid improves the retention of fine particles in the web. The additive may be cationic polyacrylamide (CPAM), whereby retention of negatively charged fines can be improved.

[027] Cellulosic fibers may comprise fibers from a kraft pulp, soda pulp, sulfite pulp, mechanical pulp, thermomechanical pulp, semi-chemical or chemo-thermomechanical pulp, recycled pulp or mixtures thereof in an amount from 0 to 99, 5% by weight, based on the dry weight of the cellulosic fibers.

[028] The present invention also relates to a paper obtained by the process as defined above. Paper has high strength with relatively low density, which is a big advantage, for example, in packaging technology. Furthermore, since the paper has low or no lignin content, the paper does not suffer from ama to the same extent as papers that do not contain holocellulose fibers. Therefore, paper can be used as a packaging material and or as a corrugated fiberboard.

[029] The present invention also relates to the use of wood-based holocellulose fibers produced by treating a wood-based raw material with an organic peroxide in a process comprising a delignification and a washing step in a process of papermaking to improve the strength of the paper. Suitably, holocellulose fibers are added after a refining step in a papermaking process.

[030] Additional features and advantages are described in the following detailed description with reference to the attached drawings.

BRIEF DESCRIPTION OF THE FIGURES

[031] Figure 1 shows the change in the height of the water meter as a function of time during the dewatering process.

[032] Figure 2 shows the curve of Figure 1 divided into two linear parts near the inflection point.

[033] Figure 3 shows a graph of the fiber length distribution.

[034] Figure 4 shows the results from the dewatering measurements with the DDA in the sheet former with closed water system.

[035] Figure 5 also shows the results of dewatering measurements with the DDA in the sheet former with closed water system.

[036] Figure 6 shows the tensile strength vs the amount of PAA, PAA CNF or CMF gen1 fibers added to the sheet produced with recirculating white water.

[037] Figure 7 shows the index of tensile strength vs density for the sheet produced with white water in recirculation.

[038] Figure 8 shows the tensile stiffness index vs. density for the sheet produced with recirculating white water.

[039] Figure 9 shows the tensile strength vs density for the sheet produced with closed white water and PAA, PAA CNF or CMF gen1 fibers added.

[040] Figure 10 shows the SCT index vs density for the sheet produced with recirculating white water.

[041] Figure 11 shows the tensile strength index vs. sheet former drainage time for the sheet produced with recirculating white water.

[042] Figure 12 shows the tensile strength vs final sheet density for lab sheets with recycled fibers and PAA, PAA CNF, CMF gen1 or CS fiber added.

[043] Figure 13 shows the tensile strength vs drain time in the sheet former for lab sheets with recycled fibers and PAA, PAA CNF, CMF gen1 or CS fiber added.

[044] Figure 14 shows the effect of the addition of holocellulose fibers on the tensile strength index.

[045] Figure 15 shows the effect of adding holocellulose fibers together with cationic starch to improve tensile strength.

[046] Figure 16 shows the SCT index for leaves produced with recirculating white water.

[047] Figure 17 shows the SCT index for sheets formed with holocellulose fibers and cationic starch.

[048] Figure 18 shows that holocellulose fibers develop strength at a lower densification rate.

[049] Figure 19 shows that the addition of holocellulose fibers gives better strength with less densification compared to refinement.

[050] Figure 20 shows that the addition of holocellulose fibers to recycled fibers (OCC) improves tensile strength and dewatering significantly.

[051] Figure 21 shows the effect of washing the RF fibers in the form of OCC.

[052] Figure 22 shows that there is little densification observed with the addition of holocellulose fibers.

[053] Figure 23 shows the effect of drying holocellulose fibers.

[054] Figures 24 and 25 show the tensile strength of films produced from CNF and CMF gen 1 based on holocellulose, respectively.

[055] Figure 26 shows the concentration of peracetic acid (a.u.) as a function of time (min) in a medium containing water, peracetic acid, acetic acid, peroxide and caustic soda.

[056] Figure 27 illustrates the consumption of peracetic acid per gram of wood given in arbitrary units in the method comprising the addition of PAA in two steps with an intermediate alkaline step.

[057] Figure 28 illustrates the consumption of peracetic acid per gram of wood given in arbitrary units in the method comprising the continuous addition of PAA.

[058] Figure 29 illustrates the chemical composition of the samples.

[059] Figure 30 illustrates a drainage time in a sheet former as a function of the increase in the tensile strength index in (kNm/kg) and as a function of the increase in the amount of holocellulose fibers in the pulp.

DETAILED DESCRIPTION

[060] One of the biggest challenges in the production of paper-based products, for example printing paper, packaging materials, tissue paper etc. all of which will be referred to as 'paper', is to increase the strength of the paper without adversely affecting the removal of water during papermaking. During the papermaking process with a conventional pulp, such as kraft, sulfate, mechanical pulp, as raw material, an increase in paper strength can, however, contribute to a decrease in dewatering during the papermaking process. For example, a common way to increase strength is to refine the pulp. The refinement step increases strength but also has a negative impact on pulp drainability. Thus, there is a long-felt need for cost-effective, energy-saving papermaking processes to produce stronger paper-based materials without adversely affecting drainability.

[061] The inventors of the present invention have found that by using holocellulose fibers in the papermaking process, paper strength can be improved while drainability is not substantially affected. However, the production costs of holocellulose fibers are high and therefore there is a desire for a more cost-effective way of producing holocellulose fibers.

[062] The inventors of the present invention have found an economical method to produce holocellulose fibers. It was surprisingly noted that for a production method involving i) continuously loading the organic peroxide into the wood-based raw material during treatment; and/or ii) loading the organic peroxide into the wood-based feedstock in at least two separate steps with an intermediate alkaline treatment step, the total amount of organic peroxide, such as peracetic acid (PAA), used for the delignification or wood in the production of holocellulose fibers can be substantially diminished compared to prior art methods in which organic peroxide is initially loaded into a reactor in a high concentration. For example, it has been found that organic peroxide can be used in a total amount of 2.0 g of organic peroxide/g of wood fibers or less, or 1.5 g of organic peroxide/g of wood fibers or less. , especially when the wood-based raw material is in the form of larger wood chips. The amount can be less than 1.3 g of organic peroxide/g of wood fibers or less than 1.0 g of organic peroxide/g of wood fibers when small wood chips, small wood veneers or matches are used. as a wood-based raw material. Production of holocellulose fibers in this context means the extraction of cellulosic fibrous material from wood-based raw material (wood), that is, the release of cellulose fibers from other chemicals and impurities in the wood. .

[063] The method may thus comprise continuously loading the organic peroxide into the wood-based raw material during treatment and/or loading the organic peroxide in at least two separate organic peroxide treatment steps with an alkaline treatment step intermediary. The intermediate alkaline treatment step may be carried out at a pH of 8 or more, for example from pH 10 to 12. The temperature may be 15 to 100°C at atmospheric pressure for a duration of at least 1 hour, such as from 1 to 3 hours.

[064] The organic peroxide can be peracetic acid (PAA). This chemical leads to a selective removal of lignin. However, the known peracetic process used to produce holocellulose fibers is cost prohibitive due to the cost of producing organic peroxide, eg peracetic acid. On a laboratory scale, the amount of peracetic acid used can be on the order of 2.5g or more of peracetic acid, expressed as pure (pure) acetic acid, per gram of wood, which is considered too high for industrial production. A more economical way of producing these fibers is therefore desirable to transpose this concept to the industry. By the solution of the present invention, the amount of peracetic acid required for industrial production of holocellulose can be reduced while the final paper product maintains similar strength properties and dewatering properties during papermaking as obtained with peracetic acid treatment. in larger quantities. In accordance with the present disclosure, organic peroxide is not overdosed in the treatment process, whereby an affordable method for producing holocellulose fibers is provided. The method is also applicable in large-scale industrial factories.

[065] In the following, the method is described in more detail with reference to peracetic acid. However, other organic peroxides may be conceivable.

[066] The treatment or reaction, therefore, may involve the use of peracetic acid and wood-based raw material, with water. Water can be used as a vehicle or solvent. The reaction can be carried out in a reactor or vessel. If the vessel is pressurized, the reaction temperature may be higher. The reaction can last for a few hours, during which the peracetic acid is consumed by the wood-based raw material. This therefore means that the concentration of peracetic acid decreases during the reaction in the vessel, unless compensated for by continuous injection, as suggested in embodiments of the present invention. The reaction can be carried out in a batch reactor or a continuous reactor.

[067] In previous tests to produce holocellulose fibers, a high concentration of peracetic acid was initially added to a reactor, which in turn generated high costs. Without being bound by any theory, it is believed that this is partly due to the spontaneous disappearance of peracetic acid at high concentrations, reacting spontaneously with itself, that is, in other molecules of peracetic acid. This behavior can also occur at lower concentrations, but to a substantially lesser extent. Thus, it was noted that by keeping peracetic acid in low concentration, at least at the beginning of the reaction, most of the peracetic acid reacts with the wood rather than reacting with itself, so the total amount of peracetic acid used is decreased and a more effective use of peracetic acid is obtained.

[068] However, by having a low concentration of peracetic acid at the beginning of the reaction, there is also a low amount of peracetic acid in the reactor. This small amount may not be enough to treat all the wood. This is why more peracetic acid can be added to the reaction. In previous attempts, a high concentration of peracetic acid is initially added to the reactor, and then it is waited until it is consumed. Subsequently, the reactor is washed and new peracetic acid is added. Instead of waiting for all the peracetic acid to be consumed before adding new peracetic acid, in accordance with an embodiment of the present invention, the peracetic acid can be added continuously by injection to the reactor. Continuously charging organic peroxide means the action of using a source of concentrated organic peroxide to constantly adjust the concentration of peracetic acid within the reactor to a predefined concentration. The main reason for this injection is to keep the concentration high enough for the reaction to proceed at a sufficient rate, but low enough that the main reactions in the reactor are those involving peracetic acid in the wood, as opposed to reactions involving peracetic acid on itself. same. In a way, the injection compensates the consumption of peracetic acid in the reactor, or allows a better control of the peracetic acid profile by adjusting its value over time to pre-established values. This continuous loading can be accomplished by the use of any type of injectors associated with a pump or any type of flow generating devices. The concentrated source of peroxide compound is preferably a concentrated/distilled peroxide compound, but may also be an equilibrium solution containing an organic acid and hydrogen peroxide and a certain amount of the associated organic peroxide or peracid (where applicable) or a diluted solution. Loading is carried out as long as peracetic acid is required to transform the wood into a material that is sufficiently delignified and/or white, for example, for the production of white wood, or that can be defibrated, for example, for the production of pulp related. Thus, the reaction will be additionally faster since there is no need to wait until the reaction is complete, which takes time as the reaction rate slows down as the concentration decreases. By continuous injection, a certain defined concentration can be maintained for a desired reaction time. Thus, a low total charge is obtained. Injection can be performed with a side pump which is arranged to inject peracetic acid at a desired charge rate into the reactor during the reaction. By low load it is meant that the total consumption of PAA is kept below 2 g PAA/g of wood. At low load, the concentration may be, for example, about 3% peracetic acid in the reactor.

[069] Peracetic acid injection or loading rate can be constant during the reaction time. Alternatively, the charge rate can be modified during the reaction. In this way, continuous charging can be performed at one or more charging rates throughout the treatment. Charge rates can be predetermined or adjusted during the reaction. For example, the injection rate or rate can be modified in case of high deviation from the defined concentration of peracetic acid given in the reactor. That is, if the concentration is higher than the defined concentration in the reactor, the injection rate is reduced, for example, by decreasing the speed of the injector. The injection rate depends on the amount of water in the reactor, which means that if there is more water in the reactor than a desired amount of water, then more peracetic acid is injected into the reactor to reach a given concentration defined in the reactor. Similarly, the injection rate depends on the concentration of peracetic acid in the peracetic acid stock solution, which is usually a distilled peracetic acid solution with a concentration of 39% to 40% peracetic acid. Another supply alternative may be an equilibrium peracetic acid solution. The injection speed can be configured to be variable and automated, depending on the concentration of peracetic acid in the reactor. In this way, it is possible to have a better control of the concentration of peracetic acid in the reactor, which in turn will provide a better control of the reaction and its speed in the reactor. The defined concentration in the reactor, i.e. a target concentration in the reactor, can be, for example, 2.5 to 3.5% peracetic acid in solution, such as 3% peracetic acid in solution. The concentration can also be adjusted to vary during the reaction, for example 2.5% in the first 2 hours and 3.5% in the next 2 hours, and end at 3.0% in the last 2 hours. The pH of the reaction can be monitored and can be maintained at a value of around pH 4. If the pH drops during the reaction, for example, caustic soda can be injected in batches or continuously into the reactor to keep the pH around 4.

[070] Thus, through the continuous injection of organic peroxide, such as peracetic acid (PAA), it is possible to maintain a low total load of PAA in the reactor. The reactor may contain the wood-based feedstock, a little water and a constant or controlled amount of peracetic acid. The reactor may additionally contain reaction degradation products, e.g. dissolved lignin and carbohydrates from wood, its by-products, the by-product of peracetic acid (acetic acid) and other chemicals, which may include hydrogen peroxide, dissolved oxygen, etc. . Therefore, it is possible to reduce the amount of peracetic acid needed for the production of holocellulose. In this way, it is possible to decrease the use of peracetic acid to a low level, for example from about 0.3 to 0.7 g of pure PAA/g of wood. This amount corresponds to a minimum amount of total oxidation and therefore lignin removal. However, holocellulose fibers can also be produced even if the lignin is not fully oxidized, but instead oxidized to a level that can be removed. The oxidation level can be determined from experiments if desired. The continuous introduction of peracetic acid is a way to guarantee the production of a product, limiting its cost. Additionally, better overall process safety can be ensured as runaway risks are limited to these lower working concentrations. On the other hand, the method that involves the use of at least two steps of PAA treatment with an intermediate alkaline step allows the partial removal of some lignin. As this lignin can be removed, there is no need to oxidize it, making it possible to achieve an even greater reduction in the use of PAA, down to less than 0.3 g pure PAA/g of wood.

[071] An analysis of reactions involving peracetic acid under conditions where a large amount of peracetic acid is initially added to a reactor shows that a high initial charge of peracetic acid leads to a high consumption of peracetic acid for unnecessary purposes, i.e., those not delignification. Figure 26 illustrates the phenomenon and shows the consumption of peracetic acid by the reaction of peracetic acid in a reactor without organic matter, in addition to peracetic acid and acetic acid. Figure 26 shows a peracetic concentration (a.u.) as a function of time (min) in a medium containing water, peracetic acid, acetic acid, peroxide and caustic soda. In Figure 26, the results are shown with black dots and a corresponding model of the reaction involving peracetic acid under process conditions in a reactor originally containing pH adjusted water and peracetic acid is shown with a dotted line.

[072] The present invention limits the magnitude of unnecessary PAA reactions with itself due to the low amount of PAA used. As described above, this can be achieved, for example, by continuously loading peracetic acid into the reactor and keeping the concentration continuously at a low concentration level. In doing so, peracetic acid is more likely to react with the lignin in the material than primarily with itself. The consumption of peracetic acid to obtain a given reaction advance is therefore reduced, which leads to a lower cost of obtaining a given product. This invention allows a significant cost reduction for the production of holocellulose, while maintaining the desirable fiber and therefore the paper properties described in the above present invention.

[073] According to another variant of the method for producing holocellulose fibers, i.e. pulping, according to the present disclosure, the alkaline treatment can be used between two stages of peracetic acid. This means that peracetic acid is used during pulping with an alkaline treatment between the two peracetic acid stages, whereby white holocellulose fibers are produced without a prior independent pulping step. Thus, the present alkaline treatment between the peracetic treatment steps is different from the alkaline treatments used in bleaching, where alkaline steps or extraction steps are performed to remove oxidized lignin from fibers that were produced in an independent pulping step. The present method therefore provides a cost-effective process with few steps.

[074] The first step of peracetic acid treatment may have a relatively high initial concentration of peracetic acid and may be without continuous injection. Alkaline treatment is carried out between the first and second peracetic acid treatment steps. The second step of peracetic acid treatment can be carried out in a similar manner to the first step of peracetic acid. Alternatively, the first and second steps of peracetic acid treatment can be carried out with a low initial concentration of peracetic acid and with continuous injection as described above. The method may comprise one or more alkali treatment steps and more than two peracetic acid treatment steps. For example, the method may comprise a first peracetic acid treatment step followed by a first alkaline treatment step, which is followed by a second peracetic acid treatment step, followed by a second alkaline treatment step, followed further by a alkaline treatment step.

[075] Before the alkaline treatment step, the reactor can be drained at the end of the peracetic acid treatment step. Reacted wood can be washed. A pH-adjusted water, which can be adjusted with, for example, caustic soda, can be added to the reactor. Alternatively, water can be added to the reactor and then the pH can be adjusted until an initial pH value is reached. The initial adjusted pH may be more than pH 9, for example from pH 10 to 12. The pH generally decreases during alkaline treatment. Suitably, a final pH can be chosen to be, for example, pH 10 or more, but is not limited thereto. Generally, to obtain the beneficial effects mentioned above, the final pH can be greater than 7. The alkaline treatment step can last an hour or more. The temperature during the alkaline treatment steps may be 15 to 100°C at atmospheric pressure, and could be, for example, 40 to 80°C at atmospheric pressure. If the alkali treatment is carried out in a pressurized vessel, the temperature may be higher. Additionally, the pH can be higher than 12 under certain conditions. Also, the duration of treatment can be adjusted to prevailing conditions and can be, for example, 5 hours or even longer. Alternatively, if the treatment duration can also be shorter, such as 10 to 30 minutes.

[076] The organic peroxide steps mentioned in the present disclosure are either two peracetic acid steps performed, for example, by loading the organic peroxide in high concentration at the beginning of the treatment and letting it react until the organic peroxide has reacted, in then rinsing the reacted wood and then adding the organic peroxide again. The procedure can be performed as many times as necessary.

[077] The temperature during the reaction with the organic peroxide in embodiments of the method for producing holocellulose fibers of the present invention may be 15 to 100°C, suitably 40 to 90°C or 55 to 75°C, for example about 70°C. The pH can be acidic, for example from 2.5 to 5, such as 4.0 to 4.8, and the pH can be adjusted by adding caustic soda. The temperature can be controlled by circulating a heated fluid around the reaction chamber with a predefined temperature profile, which can vary, for example, gradually increasing from 40 to 70 degrees Celsius. Alternatively, the organic peroxide steps can be performed with the continuous loading concept described above. For example, continuous charging can be carried out so that the peracetic acid concentration is maintained at a value of 3%, with continuous pH adjustment and at a temperature of 60°C or 70°C adjusted with a heated liquid. In this way, the consumption of peracetic acid can be reduced while the reaction time is kept relatively short.

[078] Without being bound by any theory, it is believed that the organic peroxide reacts with the lignin in the wood-based raw material, through which part of the lignin can be solubilized. However, part of the lignin that is oxidized by the organic peroxide may remain bound to the fibers and may continue to use the organic peroxide. This oxidized lignin can be solubilized under alkaline conditions. Thus, the two-step treatment with organic peroxide, which may be peracetic acid, with an intermediate alkaline step refers to improving the efficiency of peracetic acid during delignification by removing some of the dissolved lignin and through solubility under alkaline conditions. of partially oxidized lignin.

[079] The removal of these two lignin fractions leads to a decrease in the need for peracetic acid to obtain a certain degree of lignin removal, see the experimental part and mainly Figures 27 and 28. The removal is an alkaline removal. For example, the removal can be by means of an alkaline treatment at a temperature of 25°C to 70°C, with an initial pH of 12, which can evolve freely during, for example, one hour, or an alkaline extraction at a temperature of 25°C, pH maintained at 12 with addition of caustic soda for for example one hour, and carried out in the present invention after a first wash with water.

[080] The amount of peracetic acid required to achieve a certain level of delignification is reduced, as can be seen in Figure 26, leading in turn to a reduced production cost of holocellulose in relation to the cost of organic peroxide. The pulps obtained after these treatments present similar properties and performances, and of similar composition, based on the analysis of carbohydrates, to those observed for the pulps treated under conditions that involve the use of peracetic acid (PAA) in the amount of 2.5 g PAA /g fibers, see experimental part and Figure 29.

[081] According to an additional variant, it is possible to combine the method with continuous loading of organic peroxide and divide the peracetic acid reaction into two reactions separated by the alkaline step, which can be an extraction step, that is, an alkaline treatment. intermediate at, for example, 70°C, for example pH 12 to 10 and for 1 to 3 hours. The consumption of peracetic acid can then reach the value of 1.1 g/g. These two ideas together led to a consumption of 0.7 g per g of wood.

[082] In accordance with a further aspect of the present invention, a method for producing a paper strength agent is provided. The method comprises the steps described above for producing holocellulose fibers either by continuous injection of peracetic acid and/or by including an alkali treatment step between the peracetic acid treatment steps. The holocellulose fibers produced may optionally be microfibrillated, as will be described in more detail below, to provide holocellulose nanofibrils (CNF). The holocellulose fibers or holocellulose nanofibrils produced are subsequently dried. In the final step, the dried holocellulose fibers or holocellulose nanofibrils are de-aggregated. The paper strength agent produced by such a method provides surprisingly strong paper, while the dewatering properties are not adversely affected.

[083] In addition to the methods described above, the inventors of the present invention have discovered an economical and efficient papermaking process that provides improved paper strength while dewatering during the papermaking process is not substantially adversely affected. In the process, a papermaking pulp is prepared which comprises an aqueous pulp slurry comprising cellulosic fibers and having a fiber consistency of 0.1 to

40% by weight, based on the weight of the paste. By fiber consistency is meant the dry content of cellulosic fibers in an aqueous pulp slurry.

[084] In accordance with the present invention, the cellulosic fibers comprise or consist of wood-based holocellulose fibers. Wood-based holocellulose fibers are produced by treating a wood-based raw material with an organic peroxide, preferably peracetic acid (PAA). Wood-based holocellulose fibers provide strong paper, while dewatering during the papermaking process is not adversely affected.

[085] The amount of wood-based holocellulose fibers can be from 0.5 to 100% by weight, based on the dry weight of the cellulosic fibers. Thus, the wood-based holocellulose fibers can be used as a constituent, i.e. an additive, in the pulp slurry comprising the cellulosic fibers or the wood-based holocellulose fibers can make up the cellulosic fibers of the aqueous pulp slurry. By using the holocellulose fibers as an additive in the pulp slurry, the strength of the paper is improved while the drainage is not adversely affected, through which an energy efficient process can be achieved.

[086] "Paper" used in this context refers to a material made from pulp, which comprises cellulosic fibers. Paper is manufactured from an aqueous slurry comprising cellulosic fibers by pressing the wet fibers together and then dewatering and/or drying the fibers into a thin, flexible material. The paper can be a single-layer product or it can contain multiple layers. By paper it is also understood, for example, printing paper, tissue paper, filter paper, paperboard and/or cardboard, including corrugated fiberboard. Cardboard, cardboard, or packaging paper is a cardboard product made from a pulp and can be made from several layers of paper. Corrugated fiberboard is included in the definition of paperboard/cardboard and refers to a material comprising corrugated sheets and one or more layers of flat backing.

[087] Tissue paper is a very thin or light paper often produced with a paper machine comprising a steam-heated drying cylinder (yankee cylinder) or air drying (TAD) of the tissue. Tissue paper often has a good absorbency, for example about 1 g liquid/1 g fiber, but may be higher or lower depending on the quality of the tissue paper.

[088] Generally, cellulosic fibers can be fibers from unbleached or bleached pulp comprising a pulp selected from a kraft, soda, sulfite, mechanical pulp, a thermomechanical pulp (TMP), a semi-chemical pulp (e.g. semi-chemical pulp) of neutral sulfite; NSSC), a recycled pulp or a chemo-thermomechanical pulp (CTMP), or mixtures thereof. Cellulosic fibers also include holocellulose fibers. The recycled pulp can be, for example, old corrugated cardboard/container (OCC). The raw material for the pulps can be based on softwood, hardwood or recycled fibers. Softwood tree species can be, for example, but are not limited to: spruce, pine, spruce, larch, cedar and hemlock. Examples of hardwood species from which the pulp useful as a starting material in the present invention may be derived include, but are not limited to: birch, oak, poplar, beech, eucalyptus, acacia, maple, alder, poplar, trees of gum and gmelina. Preferably, the raw material mainly comprises softwood. The raw material may comprise a mixture of different softwoods, for example pine and spruce. The raw material can also be a non-woody raw material such as bamboo and bagasse. The raw material can also be a mixture of at least two softwoods, hardwoods and/or non-woods.

[089] Cellulose nanofibril (CNF) in this application is sometimes referred to in the literature by the terms nanofibrillated cellulose (NFC), nanofibrillary cellulose (NFC), microfibrillated cellulose (MFC), microfibrillary cellulose (MFC), cellulose microfibril (CMF) and Cellulose nanofiber (CNF). These terms are similarly used and describe cellulose nanofibrils produced by mechanical treatment of plant/wood-based materials and may be combined with chemical or enzymatic pre-treatment steps. Mechanical treatment includes mechanical microfibrillation of fibers and can be performed, for example, by high pressure or ultrasonic homogenizers, crushers or microfluidizers, which expose the fibers to high shear forces. In this way, the fibers are torn into nanofibrils. Generally, cellulose nanofibrils are composed of at least one elemental fibril containing crystalline, paracrystalline and amorphous regions, with an aspect ratio generally greater than 10, which may contain longitudinal divisions, entanglement between particles or network structures. Aspect ratio refers to the ratio of the longest to the shortest dimensions. Dimensions are typically 3-100 nm in cross section and typically up to 100 μm in length. Cellulose nanofibrils produced from plant sources by mechanical processes usually contain hemicellulose and, in some cases, lignin. Some cellulose nanofibrils may have functional groups on their surface as a result of the manufacturing process. The term cellulose nanofiber has been used to describe cellulose nanofibrils from bacterial sources. Cellulose nanofibril can be defined according to ISO/TS 20477:2017(en).

[090] In the process of the present invention, the step of preparing the papermaking pulp may comprise a step of adding an additive to the aqueous slurry, beating and/or refining an aqueous slurry. In one embodiment, the additive may comprise a holocellulose CNF, i.e. cellulose nanofibrils produced from holocellulose fibers. In this way, additional improved strength properties can be obtained while dewatering is not impaired. The holocellulose CNF can be added in an amount of 0.1 to 10% by weight, or 0.5 to 5% by weight, based on the dry weight of the pulp.

[091] Holocellulose is the total fraction of cellulose and hemicellulose in wood and makes up 65 to 75% by weight of the fiber weight. Holocellulose is obtained by removing extractives and lignin from the original natural wood material, whereby holocellulose fibers are obtained. Holocellulose fibers are therefore cellulosic fibers. The holocellulose in the present invention is wood-based and can be produced by deligning wood with acid-chlorite or peracetic acid (PAA). Holocellulose can be used to produce cellulose nanofibrils (CNF) and hence by holocellulose CNF means cellulose nanofibrils produced from holocellulose. Unlike other fibers with lower hemicellulose content, for example, alkali treated fibers, fiber drying does not appear to affect the subsequent nanofibrillation step. Furthermore, films produced from holocellulose CNF exhibit excellent mechanical properties. By using wood-based holocellulose fibers, the strength properties of the produced paper can be improved while the dewatering properties are not impaired, which is a significant advantage in the papermaking process.

[092] The process for producing paper generally comprises the steps of pulp preparation, feeding the pulp comprising an aqueous slurry of cellulosic fibers to a forming section of the paper machine to form a web and dewatering the web. The pulp preparation may include a step of adding different additives to a pulp comprising cellulosic fibers. In addition, the pulp is often mechanically treated by refining and/or beating. In the pulp preparation step, different pulps can be mixed to form an aqueous pulp slurry suitable for use in the paper machine. Cellulosic fibers comprise or consist of holocellulose fibers produced by treating a wood-based raw material with an organic peroxide. The organic peroxide may be peracetic acid. Peracetic acid has the advantage of being selective, but it does not oxidize many carbohydrates. The amount of wood-based holocellulose fibers is from 0.5 to 100% by weight or from 0.5 to 80% by weight or from 2 to 60% by weight or from 4 to 55% by weight, based on the total weight of cellulosic fibers. In one embodiment, the amount of wood-based holocellulose fibers is from 25 to 50% by weight of the cellulosic fibers.

[093] After the slurry comprising an aqueous pulp slurry is prepared, it is fed to a screen forming section where a web is formed. Dewatering is a procedure by which water is removed from a web of wet pulp. Dewatering can be carried out mechanically during web formation in a yarn, for example by means of pressure, vacuum or centrifugal forces. Dewatering can also be carried out partially in a press section of a paper machine by means of mechanical forces, for example by pressing. After dewatering on a screen and/or a pressing section, the web can be routed to a drying section, where the water/moisture remaining in the web is evaporated by heat, also called thermal dewatering. The drying section can be designed in different ways and may comprise, for example, multi-cylinder dryer, Yankee cylinder drying, direct drying or flash drying equipment.

[094] Moisture content means the water content of the material expressed in % by weight and based on the total weight of the material.

[095] In order to increase paper strength, there are several different groups of additives suitable as dry strength aids, including, but not limited to, nanocellulosic materials such as microfibrillary cellulose, cellulose nanofibrils, cellulose filaments, cellulose nanocrystalline, fines or enriched with fines - pulps including holocellulose CNF and preferably wood-based holocellulose CNF, charged or uncharged starch such as cationic starch, gum derivatives, synthetic copolymers with acrylamide such as acrylic acid, vinyl pyridine , 2-aminoethyl methacrylate, diallyl dimethyl ammonium chloride, dimethylaminopropylacrylamide, diamine ethyl acrylate, styrene and glyoxalated polyacrylamides. The latter group is also suitably copolymerized with cationic monomers. By using cationic starch as an additive along with holocellulose fibers, synergistic strength-enhancing effects can be obtained with low levels of starch addition. The cationic starch may be added in an amount of less than 10% by weight, for example from 0.5 to 5% by weight, or from 0.8 to 3% by weight, based on the dry weight of the pulp. Especially advantageous effects can be obtained if the cellulosic fibers can comprise holocellulose fibers from 0.5 to 80% by weight or from 2 to 60% by weight or from 4 to 55% by weight or from 20 to 30% by weight.

[096] Additives referred to as wet strength agents or resins, such as urea-formaldehyde resins, melamine-formaldehyde resins, or polyamide-amine-epichlorohydrin resins, are also useful for increasing the dry strength of fibers. Such dry strength aids or wet strength resins are suitably added to the pulp slurry during paper production, whereby the strength of the final paper or board product can be improved. Retention agents can also be used, alone or in combination. Retention agents can be chosen from polyacrylamide (PAM), which can be cationic (CPAM), polyethyleneimine (PEI), colloidal silica (CS), which can be negatively charged, bentonite and combinations thereof. The retention aid may be added in a total amount of from about 1 to 50,000 g/ton, for example, in an amount of 100-5000 g/ton, based on the weight of the pulp.

[097] Additional advantages and characteristics of the present invention are described in the following examples, which should not be considered as limiting the scope of the present invention. Examples

[098] Additional effects and advantages obtained by the present invention are illustrated in the experimental part of the description below. The effect of adding holocellulose fibers or CNF, which were treated with peracetic acid (PAA), as a dry strength agent on laboratory sheets was investigated. PAA-treated holocellulose fibers were referred to as PAA fibers and PAA-treated cellulose nanofibrils were referred to as PAA CNF. The effect of strength agents on yarn dewatering in the sheet former and the tensile properties of the final sheets were studied. materials

[099] Table 1. Materials and chemicals used in the study.

Description Product Company Bleached softwood kraft Södra green unrefined (SBK) Södra Recycled fiber (RF) - DS Smith Peracetic acid fiber (PAA) RISE Innventia

(Birch) AB Cellulose Nanofibrils PAA RISE Innventia (CNF, Birch) AB RISE Innventia Cellulose Microfibrils (CMF) Generation 1, Pilot AB Cationic Starch (CS) Amylofax pw Avebe Cationic Polyacrylamide (CPAM) Fennopol KF430T Kemira Silica Fennosil 900 Kemira Bentonite Hydrocol OM Axchem

[100] Bleached unrefined softwood kraft (SBK, Södra green) was shredded in accordance with ISO 5263-1 as valid on the priority date of this application. The SBK was refined to two levels at 200 and 400 kWh/ton using a Voith laboratory refiner (segment 3 at 1.0 at 60) and the Schopper-Riegler values were 24 and 63, respectively.

[101] The recycled pulp was prepared by stripping test liner (DS Smith) according to ISO 5263-1 and contained 14 wt% filler. Two separate sets of experiments were carried out, one using the de-aggregated pulp in its original form and the second where the pulp was washed in order to remove the filler and anionic waste from the pulp. The broken down recycled fibers were washed by 1) adjusting the suspension to pH 2 with hydrochloric acid (HCl), after 30 min the suspension was filtered (100 µm screen) 2) washing with 10 L of acidic water (HCl, pH 2) 3) wash with deionized water until the conductivity in the filtrate is less than 5 µS/cm 4) adjust the concentration of sodium carbonate (Na2CO3) to 0.001 M 5) after 10 min, the suspension was adjusted to pH 9 with sodium hydroxide (NaOH) 6) after 30 min, the pulp was washed with deionized water until the conductivity in the filtrate was less than 5 µS/cm. The filler content in the washed recycled pulp was 3.6% by weight.

[102] Holocellulose fibers were produced with peracetic acid (PAA) treatment with two pretreatment steps, a delignification step and a washing step. The fibers are referred to in the present invention as PAA fibers. In the first pre-treatment step, the wood chips (Birch, 35 g) were soaked in water and placed under vacuum until they no longer float. Subsequently, the chopped fibers were treated with an acetone/water solution to remove the extractives. In the second pre-treatment step, the fibers were added to a solution of diethylenetriaminepentaacetic acid (0.3% by weight)/sodium sulfite (4% by weight) (pH, 6.85ᵒC) and allowed to react for 1 h in nitrogen atmosphere. The solution was cooled and filtered, and this step was repeated until the conductivity was less than 5 µS. In the delignification step, the wood chips were immersed in 800 mL of 10% PAA solution adjusted to pH 4.8 with NaOH. The suspension was heated to 85 °C and allowed to react for 1 hour. To stop the reaction, the suspension was cooled and filtered. The PAA delignification step was repeated three times before thinning the fibers with 5000 revolutions. In the washing step, the pulp suspension was adjusted to pH 12 with NaOH, after two hours the pulp was washed with deionized water until the conductivity was less than 5 µS, izothiazoline biocide (0.2 mL/L) was added to the pulp suspension. The total amount of PAA used was 2.08 - 2.03 g PAA/g wood, ie more than 2 g PAA/g wood.

[103] PAA CNF holocellulose was produced by homogenizing the never-dried PAA holocellulose fibers (3.3% by weight) with a homogenizer (M-110 EH, Microfluidics) at 1700 bar and a passage through the chamber of 200 µm and 100 µm at 1700 bar. The PAA fibers were readily fibrillated and no pre-treatment of the fibers was necessary. The same homogenization procedure was used to produce PAA CNF from dried PAA fibers.

PAA fibers (30 g, dry basis) were dried in a ventilated oven for 4 h at 90 ᵒC and again disaggregated according to ISO 5263-1.

[104] CMF, referred to as RISE Innventia AB generation 1 pilot or CMF gen1, was produced from never-dry, sulfite-bleached softwood pulp that was pre-treated by refining twice with an enzyme treatment step (FiberCare® , Novozymes, Denmark) intermediate. The pre-treated pulp was homogenized by passing through a pilot homogenizer (GEA, Ariete NS3034, Niro Soavi) at 1200 bar. methods

[105] This study was divided into two parts with different mixtures of inputs. In the first part, laboratory sheets were produced with SBK, the unconditioned weight was 100 gsm. The effects on the dewatering capacity of the pulp and on the physical properties of the sheets were investigated with the addition of fiber PAA, PAA CNF, CMF gen1, CS or pulp refinement.

[106] Lab sheets were produced with either an open or closed white water system. The retention of fines and dry strength agent added to the lab sheets with closed white water system were controlled by building a white water balance. For test points with SBK and an open white water system, retention of added fines and dry strength agents was aided by the addition of 500 g/ton CPAM and 600 g/ton silica.

[107] The effect of pulp drying was investigated, lab sheets were produced from unrefined SBK or PAA fibers that were dried and shredded. Laboratory sheets with SBK were produced from pulp that was dried and shredded once (OD) or twice (TD). Laboratory sheets with PAA fibers were produced from pulp that was either never dried (ND) or dried once (OD) and shredded.

[108] In the second part of the study, laboratory sheets were produced with recycled fiber (RF), also called OCC (old corrugated container), whose unconditioned weight was 120 gsm. The effects on yarn dewatering and physical properties of sheets were investigated with the addition of PAA, PAA CNF, CMF gen1 or CS fiber. The lab sheets in the second part were produced with a closed white water system. Lab sheets were produced with either 1) washed RF with low filler content (3.6% by weight) and no retention aid or 2) crumbled RF that contained 14% filler by weight, to these test points were added 200 g/ton of CPAM and 4000 g/ton of bentonite.

[109] PAA CNF was produced by homogenizing either never-dried or dry and crumbled PAA fibers. Homogenization corresponds to the mechanical microfibrillation of the fibers. The reinforcing effect with addition of PAA CNF produced from never-dried (ND) or once-dried (OD) PAA fibers was compared with RF-disaggregated laboratory sheets. Furthermore, the films were produced with 100% PAA CNF (ND), PAA CNF (OD) or CMF gen1 and their tensile properties were evaluated, the film weight was 30 gsm. Table 2 below shows a summary of the test points in the study. The leaves were produced with an open or closed white water system, as explained below. The properties that were evaluated were tensile (tensile) properties, dewatering sheet former (DSF), dynamic drainage analyzer (DDA) and short compression test (SCT). The effect of drying and unbundling was investigated for SBK, PAA fiber and PAA CNF, where ND is never dry, OD is never dry and TD is twice dried. Water Leveling Agent Auxili Polp Gramat Method/Property Addition Resistance/Variable Whiteness of Dry A ura ities Retention Ability Reference Sheet Closes SBK 100 Laboratory No.

DDA Sheet of 2, 5, 25, 50, Close Fiber PAA SBK 100 Laboratory number, 100% of

DDA Closing Sheet PAA CNF 2, 5, 10% SBK 100 Laboratory No.

DDA Closing Sheet CMF gen1 2, 5, 10% SBK 100 Laboratory No.

DDA Refining Closure Sheet SR 24 and 63 SBK 100 Laboratory No.

DDA Open CS Sheet CS: 0- 5% SBK 100 Yes the laboratory Fiber 25%, CS: 0 to Open Sheet SBK 100 Yes PAA/CS 5% to laboratory PAA Open Sheet SBK 100 Yes CNF/CS to laboratory CMF Open Sheet of 5%, CS 0 to 5% SBK 100 Yes gen1/ CS the laboratory PAA CNF 2, 5, 10% SBK 100 Open Yes Sheet of the laboratory,

DDA Open sheet CMF gen1 2, 5, 10% SBK 100 Yes laboratory, the

DDA Abert Sheet of - OD/TD SBK 100 o laboratory Fibr Abert Sheet of - ND/OD to 100 o laboratory

PAA Reference Sheet Closes RF 120 Yes laboratory, from

DDA Closure Sheet Fiber PAA 10, 25% RF 120 Yes laboratory, do

DDA Sheet of PAA CNF, Close 2, 5% RF 120 Yes laboratory, ND do

DDA Sheet of PAA CNF, Close 2, 5% RF 120 Yes laboratory, OD of

DDA Closing Sheet CS 0.8 .1.5% RF 120 Yes laboratory, do

DDA Close CMF sheet gen1 2, 5% RF 120 Yes from the laboratory,

DDA PAA Sheet CNF/ Close RF 120 Yes laboratory, CS do

DDA RF Closure Sheet Ref lava 120 laboratory, from the DDA RF Closure Sheet PAA CNF 5% lava 120 laboratory, from the DDA RF PAA Sheet CNF/ Closure 5/ 1.5% lava 120 laboratory, CS from the DDA PAA CNF, - 30 - Film

ND PAA CNF, - 30 - Film

OD CMF gen1 - 30 - Film

[110] The dosing strategy:

1. Add dry strength agent, mix 30s

2. Add CS, mix 120 s

3. Add CPAM, mix 30 s

4. Add microparticle, mix 30 s

[111] The dry strength agent added was PAA fiber, PAA CNF or CMF gen1. The added microparticle was silica for the SBK test points and bentonite for the recycled fiber test points. The dosing step was applied only if the test points contained dry strength agent,

CS or retention aid. Evaluation of pulp properties

[112] The following properties were evaluated for the pulps: • Schopper-Riegler (SR): ISO 5267-1 • Water retention value (WRV): SCAN- C62:00 • BDDJ fines content <76μm: SCAN-CM 66:05

[113] Fiber length distribution was measured using L&W FiberTester. The Z potential of the pulp was measured with the Zeta Potential Meter SZP-10 System (Mütek). lab sheets

[114] Laboratory sheets were produced with two methods, conventional sheet former with open or closed water system. Open water system lab sheets were produced in accordance with ISO 5269-1. Laboratory sheets with a closed water system, ie white water with recirculation, were produced in accordance with ISO 5269-3. An advantage of using a closed system is that fines retention and filling can be controlled creating a balance in the white water system. Ten sheets have been prepared to produce a retention balance, these sheets are discarded and not used in the paper test. Dewatering in sheet former

[115] Dewatering in the sheet former was analyzed by tracking the height of the water meter with an Ultrasonic sensor, UC500-L2-U-V15 from Pepperl-Fuchs. In the method, the dewatering speed and dewatering time of a sheet making process in a Finnish former are evaluated. The height of a water column was measured in real time until all the water was drained from the Finnish former and only one sheet of paper was left on the wire. The term “dewatering velocity” is referred to as the velocity that the fiber suspension has when flowing from the sheet former, and is measured in [m/s] and takes into account the entire time that the dewatering process lasts. This time is referred to as "dewatering time" and is measured in seconds and the method is further described in the Master's Thesis: "The influence of dewatering speed on formation and strength properties of low grammage webs", by Pulgar H, Tysen A, Vomhoff H, Brannvall E.

[116] Figure 1 in the accompanying drawings shows the change in water gauge height as a function of time during the dewatering process. The example shows dewatering for five sheets from a test point with a closed white water system. leaves no. 1 to 10 were produced only to build balance in the white water system and were not used to analyze dewatering or evaluate final sheet properties.

[117] There was no distinct point where the web could be considered completely drained. Therefore, the curve was divided into two linear parts near the inflection point and the drainage time was extracted by taking the intercept between the linear trend lines, see Figure 2. The drainage time for a test point was determined by taking the average of five measurements. Dewatering with DDA Dynamic Drainage Analyzer

[118] Dewatering was analyzed using the Dynamic Drainage Analyzer (DDA) 5 (Pulpeye). The same mixing speed and contact time between chemical additions were used in the production of laboratory sheets and in the measurement of DDA. The pulp consistency was 5 g/L the initial vacuum was 250 mbar. Physical properties of sheets of paper

[119] The following properties were evaluated for the lab sheets: • Weight: ISO 536 • Thickness: ISO 534:2011 • Density: weight ISO 536/thickness ISO 534:2011 • Tensile properties: ISO 1924-3 • Test of short compression (SCT): ISO 9895 • Ash content (525 ᵒC): ISO 1762 Test results

[120] The drainability of the pulps was analyzed by the Schopper-Riegler (SR) measurement and the degree of fiber swelling was analyzed by the measurement of the water retention value of the pulps (WRV). The degree of fiber swelling correlates well with the strength of the final paper. Furthermore, the degree of fiber swelling will affect press dewatering and it is known in the prior art that a higher WRV correlates with a lower dry matter content after wet pressing. At the same level of drainability, PAA fibers showed a high degree of fiber swelling when compared to unrefined bleached softwood (SBK) kraft. Fiber swelling for SBK pulp could be improved by refining but would deteriorate pulp drainability, see Table 3. SBK refined to SR 63 had only a slightly higher WRV compared to pulp refined to SR 24. when the final sheet properties or dewatering properties were analyzed, the beat comparison was made with the test points containing SBK refined at 24.

[121] It should be noted that the standard for WRV (SCAN-C 62:00) is limited to samples with cellulose fibers. Therefore, the WRV for recycled pulps, CMF or CNF materials is not measured according to the standard, the WRV for these materials still gives an indication of how their properties differ.

[122] The pulps were characterized using the L&W fiber tester (Lorentzer & Wettre), which measures fiber length, width, fines (P&S), aspect ratio, macrofibrils and roughness by image analysis. Figure 3 shows a graph of fiber length distribution, weighted length, measured with L&W fibretester. PAA fibers contained 5.5 to 6.8% by weight of fines, which is defined as the fraction of particles with a length of 0 to 0.1 mm. The pulps were also characterized by the shape factor, which is a measure of how straight the fibers are, a higher shape factor corresponds to a straighter fiber. PAA fibers had a form factor of 96.6%, which can be compared to softwood pulp, which generally has a form factor in the range of 80 to 90% and 85 to 95% for mechanical pulps.

[123] PAA CNF had lower fines content compared to CMF gen1, but WRV was three times higher.

[124] Table 3 below shows that pulp properties were characterized by measuring Schopper-Riegler (SR), water retention value (WRV), Fibertester format factor (FT), fines content (FT), fines content, britt dynamic drainage bottle (BDDJ) and fill content.

Material SR WRV Kinks Factor, Content Content Fine, fine, fill, FT FT BDDJ nto Kinks/m % in % in % % m weight SBK weight not 11.9 0.61 0, 89 83.10 6.90 5.17 Refined 3 SBK 23.8 0.33 1.61 86.10 5.20 8.87 Refined 0

SBK 63.0 0.35 2.00 86.10 7.90 14.42 Refined 0 Fiber 0.32 recycled 42 0.99 91.85 26.80 14.00 (RF) Washed RF 1.19 91.90 0.29 23.30 3.60 12.9 0.02 Fiber PAA 1.54 96.60 6.70 3.75 4 PAA CNF 9.42 45.23 CMF gen1 2.96 69.36 Kraft pulp, dewatering and sheet properties Lab sheets with SBK and without retention aid

[125] Dewatering was characterized by measuring the drainage time in the sheet former and with the dynamic drainage analyzer (DDA) as described above. If we compare the two methods that were used to measure dewatering, it is evident that the drainage time was longer in the leaf former. This can be explained by the fact that the leaf former has a greater volume of drained water (≈10 liters) in relation to the DDA (0.5 L). It should be noted that there were also differences in grammage and vacuum applied in the two methods. However, the results of dewatering measurements in the sheet former and with the DDA show similar trends, see Figure 3 and Figure 4.

[126] Drainage time increased rapidly with the amount of micro or nanocellulose particles added, CMF gen1 or PAA CNF. The negative effects on dewatering with the addition of PAA CNF and CMF gen1 can be explained by their small size, allowing them to be redistributed by the flow of water in the porous wet fiber web. There is a likelihood that the small particles become mechanically entangled as they pass through the channels in the wet web, thus blocking the channels and inhibiting the flow of water through them. This is referred to as the “choke point hypothesis” and an accumulation of small particles in the wet web will lead to increased dewatering resistance.

[127] The addition of PAA fibers did not affect yarn dewatering in the sheet former when compared to the unrefined SBK reference. This finding is corroborated by the result of the Schopper-Riegler drainability measurements, where the pulps presented similar values.

[128] Figure 3 shows the effect on drainage time with addition of PAA, PAA CNF or CMF gen1 fibers in the dynamic drainage analyzer (DDA) and sheet former (SF) for laboratory sheets with closed water system, that is, recirculating white water. Figure 4 shows the effect on drainage time with addition of PAA CNF or CMF gen1 on the dynamic drainage analyzer (DDA) and sheet former (SF) for laboratory sheets with a closed water system, i.e. white water from recirculation.

[129] Additionally, tensile strength increased with increasing addition of PAA, PAA CNF and CMF gen1 fibers, see figure 6. It can be seen that the development of strength was more efficient with PAA CNF compared to PAA and CMF fibers. CMF gen1, ie higher tensile strength at a lower addition level. Figure 6 shows the tensile strength vs the amount of PAA, PAA CNF or CMF gen1 fibers added to the sheet produced with recirculating white water. Error bars are the standard deviation. The test stitch with 100% PAA fiber was made from the second batch.

[130] As expected, the increase in tensile strength with the addition of strength additives densified the sheet, see Figure 18. The development in tensile strength and density for PAA CNF and CMF gen1 followed that of beating. The sheets with PAA fibers deviated and presented different strength and density development, at the same level of resistance, the sheets with PAA fibers presented greater volume in relation to PAA CNF, CMF gen1 and beat. The tensile strength for the PAA fiber test points increased linearly with addition levels, however, the density did not increase. Lower levels of PAA fiber addition (0-50% by weight) had a relatively small effect on density compared to the sheet with 100% PAA fiber. The addition of 50% by weight of PAA fiber resulted in an absolute increase in density and tensile strength of 41 kg/m3 and 34 kNm/kg, respectively. On the other hand, the sheet with 100% PAA fiber had a 220 kg/m3 increase in density and a 100 kNm/kg increase in tensile strength compared to the reference with 100% unrefined SBK, see Figure 7. This result indicates that 1) PAA fibers collapse readily and 2) addition of kraft fibers to PAA pulp can provide structural rigidity to the wet web, preventing it from collapsing during pressing. Figure 7 shows the tensile strength vs density index for the sheet produced with recirculating white water. Data labels are the added weight percentage of dry strength agent, labels are positioned below the marker for CMF gen1, above the marker for PAA CNF, and to the left of the marker for PAA fiber.

[131] Tensile stiffness and tensile strength had similar development, stiffness increased with density for PAA CNF and CMF gen 1 and followed the same trend as beat. Sheets with PAA fibers showed higher stiffness, at the same density level, compared to PAA CNF, CMF gen1 and beat, see Figure 8. The tensile strength was improved by the addition of PAA CNF and CMF gen 1, but decreased slightly with the addition of PAA fibers, see Figure 9.

[132] The test points with PAA fiber showed high stiffness and low strain at break, interestingly, on the other hand, sheets with PAA CNF showed high tensile strength. The difference in how tensile strength and stiffness develop with the addition of PAA or PAA CNF fibers shows the importance of the addition level and sizes of PAA pulp to the final properties of the sheet. Figure 8 shows the tensile stiffness vs density index for the sheet produced with recirculating white water. Error bars are the standard deviation. The data labels are the percentage by weight of dry strength agent added, labels are positioned below the marker for CMF gen1, above the marker for PAA CNF and to the left of the marker for PAA fiber. Figure 9 shows the tensile strength vs density for lab sheets with closed white water and added PAA, PAA CNF or CMF gen1 fibers. The data labels are the added weight percentage of dry strength agent, labels are positioned to the left of the marker for CMF gen1, to the right of the marker for PAA CNF, and above the marker for PAA fiber.

[133] Sheets with PAA CNF CMF gen1 and PAA fibers had, at a given density level, higher SCT strength compared to refinement, see Figure 10. Figure 10 shows the SCT index vs density for the sheet produced with water white in recirculation. Error bars are the standard deviation. The data labels are the percentage by weight of dry strength agent added, labels are positioned below the marker for CMF gen1, above the marker for PAA CNF and to the left of the marker for PAA fiber.

[134] In Figure 11, the tensile strength is plotted against the drain time for lab sheets with recirculating white water. The strength of the sheets with PAA fiber increased with the addition level without impairing the dewatering of the yarn. Leaves with PAA CNF had improved dewatering resistance for a given level of resistance when compared to leaves with CMF gen1. The effect on tensile strength and drainage time with addition of 2 and 5 wt% CMF gen1 or PAA CNF appears to follow a similar trend to refinement. However, at higher addition levels (10% by weight) of CMF gen1 or PAA CNF, the negative effects on yarn dewatering were more severe and the development of tensile strength and dewatering was lower than that of refinement. Impaired yarn dewatering with a higher level of CMF or CNF addition can be explained by the accumulation of small cellulose particles close to the yarn that decrease the permeability of the web. Figure 11 shows the tensile strength index vs. sheet former drain time for sheet produced with recirculating white water. The data labels are the percentage by weight of dry strength agent added, labels are positioned below the marker for CMF gen1, above the marker for PAA CNF and to the left of the marker for PAA fiber.

[135] Sheets with holocellulose fibers had significantly higher strength than, for example, refined SBK at the same density level.

[136] The sheet structure will be consolidated during forming, pressing and drying, of the wet web as the web consolidates the fiber-fiber interaction increases which strengthens the network. The greatest increase in dry strength for the fiber network is attributed to the removal of water in the drying process. The forces acting on the fibers during drying help facilitate fiber-fiber junctions to form and develop strength in the web, but also causes the web to shrink and can lead to visible defects. The sheet with highly refined SBK had high strength (101 kNm/kg) but also visible defects from the drying process. However, the sheet with 100% PAA fibers had higher strength (120 kNm/kg) compared to highly refined SBK and no visible defects. One possible explanation is that PAA fibers collapse to a greater degree on pressing, increasing the dry matter content after pressing and improving fiber-fiber interaction in the wet web. The lower dry matter content in the wet sheet after pressing can potentially decrease the forces acting on the sheet during drying and allow the formation of a more rigid fiber network with greater resistance to deformation.

[137] Figure 12 shows the tensile strength vs final sheet density for lab sheets with recycled fibers and added PAA, PAA CNF, CMF gen1 or CS fiber. The sheets were produced with a closed white water system and 200 g/ton CPAM and 4000 g/ton bentonite. PAA CNF was produced from never-dried (ND) or once-dried (OD) PAA fibers. The data labels are the added weight percent of dry strength agent, labels are positioned to the left of the markers for PAA and PAA CNF (OD) fiber and to the right of the marker for PAA CNF (ND), CMF gen1 and CS.

[138] Figure 13 shows the tensile strength vs sheet former drain time for lab sheets with recycled fibers and added PAA, PAA CNF, CMF gen1 or CS fiber. The sheets were produced with a closed white water system and 200 g/ton CPAM and 4000 g/ton bentonite. PAA CNF was produced from never-dried (ND) or once-dried (OD) PAA fibers. The data labels are the added weight percent of dry strength agent, labels are positioned to the left of the markers for PAA and PAA CNF (OD) fiber and to the right of the marker for PAA CNF (ND), CMF gen1 and CS.

[139] Figure 14 shows that the addition of 25 or 50% by weight of holocellulose fibers increases the tensile strength by 75% or 150%, but does not impair dewatering. It can also be seen that sheets with CNF of holocellulose fibers get a better strengthening effect in a given drainage compared to CMF gen1; or better dewatering at a given resistance level.

[140] Figure 15 shows that holocellulose fibers (PAA fibers) in an amount of 25% by weight of the fibers together with cationic starch (CS) added in an amount of 1% by weight and 1.5% by weight , based on the dry content of the pulp, provide a synergistic effect with respect to improved tensile strength at already low starch addition levels.

[141] Figure 16 shows the SCT index for leaves produced with recirculating white water. It can be seen that the development in SCT with the addition of holocellulose fibers in the amount of 2 to 50% by weight, based on the dry content of the pulp, followed the same trend of tensile strength.

[142] Figure 17 shows the SCT index for sheets formed with holocellulose fibers in an amount of 25% by weight and cationic starch in amounts of 0.5 to 5% by weight, both based on the dry content of the pulp. It can be seen that the development in SCT with the addition of holocellulose fibers and cationic starch followed the same trend of tensile strength.

[143] Figure 18 shows that holocellulose fibers develop strength at a slower rate of densification.

[144] Figure 19 shows that the addition of holocellulose fibers gives better strength with less densification compared to refinement (Beat: 199, 399 kWh/t; SR 24 and 63).

[145] Figure 20 shows that adding holocellulose fibers to recycled fibers (OCC) improves tensile strength and dewatering significantly. It can be seen, however, that holocellulose CNF also improves strength, but less so than holocellulose fibers.

[146] Figure 21 shows that by washing RF fibers in the form of OCC (ie, removing filler and fine material from the OCC), holocellulose CNF provides significant improvements in strength.

[147] Figure 22 shows that there is little densification observed with the addition of holocellulose fibers. The addition of holocellulose CNF provides a significant improvement in strength, but with some densification.

[148] Figure 23 shows the effect of drying holocellulose fibers. It can be concluded that there appears to be no essential hornification of the fibers and therefore no essential loss of strength when the fibers are dried. This can be seen when the effect is compared between holocellulose and SBK fibers.

[149] Additionally, CNF films were produced and the tensile strength and stiffness of the films were measured after drying. From figures 24 and 25, it can be seen that better results are obtained by the holocellulose-based CNF compared to the gen1 CMF. Examples - production of holocellulose fiber

[150] All experiments were conducted in glass reactors, with internal effluent recirculation, temperature control (via circulation of heated fluid in an envelope) and pH adjustment via on-demand injection of caustic soda. Some experiments called “continuous injection” also had a continuous injection of peracetic acid, consisting of a pump, injecting peracetic acid continuously at pre-programmed rates. In some cases, the injection of caustic soda was also programmed, at values of the order of 0.26 mL/min of a 30% caustic soda solution.

[151] All experiments were terminated prior to defibering with an extra washing procedure comprising the following steps: an alkaline step, in which the liquor to wood ratio was approximately 7.5 with an initial pH of 12 and a final pH above of 10, at an ambient temperature of about 20 °C, the duration was 30 to 60 minutes, and three washes with water, of 10 to 20 minutes each, with a liquor to wood ratio of around 7.5.

[152] Measurements were made in a similar manner as described above in the previous experimental section starting on page 20. Reference pulp

[153] The reference pulp is referred to as SD.BV.16 and was produced with only 2 consecutive peracetic acid stages, where all the peracetic acid was loaded into the reactor from the start of the reaction. This batch of 130g of wood in small chips involved a first peracetic step with 88g of peracetic acid, in about 975g of water, and the constant adjustment of the pH with sodium hydroxide was made to a pH value of 4 to 4.40 . The temperature was gradually increased from 21 to 84 degrees Celsius during 5 hours of reaction. The liquid phase was then removed from the reactor. Another peracetic acid solution was then added to the reactor (including 88g of pure peracetic acid, 780g of water and caustic soda for pH adjustment) and the pH was maintained between pH 4 and 4.35 with an addition of caustic soda on demand. The temperature rose from 21 to 78 degrees during the 4.5 hours of the reaction. A washing procedure involving water and caustic soda was then started. A total of 1.36 g (PAA) per g (wood) was loaded into the reactor. Pulps according to the present invention SD.BV.06, continuous addition of PAA

[154] The SD.BV.06 sample was performed on 90 grams of wood chips of the same size as used in the production of the reference pulp SD.BV.16 and involved only one stage of peracetic acid with continuous injection. The wood was placed in a double envelope reactor for temperature control. The temperature was set at 80 °C. The pH was adjusted with caustic soda injection to maintain the pH value between 4 and 4.35. The peracetic acid injection was adjusted so that the peracetic acid concentration did not exceed 3% in the reactor. The injection speed was performed with a Harvard pump, with a speed set at 100 mL per hour. The peracetic acid supply was 40% distilled peracetic acid. In SD.BV.06, 0.98 g (PAA) per g (wood) was consumed. SD.BV.07, continuous addition of PAA

[155] The sample SD.BV.07 in your project is a duplicate of SD.BV.06 performed at a lower temperature. 90 g of wood were placed in the reactor containing 675 mL of water, and kept at 60°C. A total of 157.9 mL of a peracetic acid stock solution was continuously injected at a rate of 50 mL/h. The total charge of peracetic acid used in this experiment is 0.75 g (PAA)/g (wood). The reaction time was about 6 hours and 25 minutes. SD.BV.05b, two-step PAA addition with an intermediate alkaline step

[156] The sample SD.BV.05b was performed on 90g of wood chips of the same size as used in the production of the reference pulp SD.BV.16, with a first step of conventional peracetic acid, in which 63 g ( expressed as pure peracetic acid) of peracetic acid was added from the beginning of the treatment (164 mL at 39%) in about 825 mL of water. The amount of caustic soda added in the experiment was to maintain the pH around 4.3 and was 55 mL of a solution with a concentration of 30%. The alkaline treatment after the peracetic acid step was carried out without prewashing the pulp and with an initial pH of 12 at a temperature of 60oC, with a liquor to wood ratio of 6. The pH was adjusted to evolve freely. The treatment was followed by a second treatment with peracetic acid, similar to the first:

Injected 164mL of peracetic acid from the start, 660mL of water and a total of 55mL of caustic soda to keep the pH at the target value. The second stage of peracetic acid was considered finished when the wood was considered white enough to be easily shredded. The first stage of the peracetic acid treatment was stopped with a low residual concentration. A calculated amount of 0.60g (pure PAA)/g of wood was consumed. The second stage of the peracetic acid treatment was considered completed with a residual amount of peracetic acid, giving a consumption value of 0.5g of peracetic acid per /g of wood. The total consumption in this experiment was therefore 1.1 g (PAA)/g (wood). SD.BV.12, two-step PAA addition with an intermediate alkaline step

[157] SD.BV.12 is inspired from SD.BV.05b. It comprises a first step of peracetic acid (110 g of wood or wood chips of the same size as used in the production of the reference pulp SD.BV.16), in 825 mL of water, and an initial charge of 165 mL of a 39% peracetic acid solution, with pH adjustment around 4.3 with 30% caustic soda). This step is followed by a water wash (10 minutes, 825 mL). An alkaline treatment is then performed (initial pH of 12, with pH adjustment to maintain pH above 10, 1.1 L of water) for 1 hour at room temperature (25-30 degrees). The wood is then washed with water (3 consecutive washes with 650 mL of water). The wood then undergoes a peracetic acid treatment (660 mL of water, initial charge of 165 mL of peracetic acid, pH adjustment with caustic soda when necessary to maintain the pH at 4.3). The last stage of peracetic acid was considered finished when the wood was considered white enough to be easily defibrated. At this point, a residual concentration of peracetic acid was measured. The total amount of peracetic acid consumed to produce this material is 0.98 g (PAA)/g (wood). SD.BV.14, two-step PAA addition with continuous charge and an intermediate alkaline step

[158] SD.BV.14 is an experiment that combines the idea of a continuous loading of peracetic acid with the idea of having an alkaline treatment intermediate between two steps of PAA. The experiment was as follows. A first step of treatment with peracetic acid (150 g of wood or wood chips of the same size as used in the production of reference pulp SD.BV.16) was carried out at 60 degrees Celsius with continuous injection of caustic soda (to maintain pH at a target of approximately 4.3), and continuous injection of peracetic acid (39% stock solution, for a total injected volume of 90 g). The injection rate was designed to be fast during the first 15 minutes to increase the concentration in the medium to about 3% (speed around 60 mL/min), and slow during the next 3 hours (20 mL/h). The wood is then washed for 10 minutes with water. The reactor is washed and an alkaline treatment is then carried out, with 1.1 L of water and a concentrated solution of caustic soda (30%) to bring the pH of the reactor to a value above pH 10 for one hour at room temperature. (about 25oC). The wood is then washed with tap water. After washing, a second treatment with peracetic acid begins, with 850 mL of water at 60oC, pH control and adjustment to a pH value of 4.3 (with a 30% caustic soda solution) and a first rapid injection of peracetic acid (13.16 mL in 15 minutes of a 39% solution) to rapidly increase the concentration in the reactor, followed by a second slower injection of peracetic acid (24 mL/h) until total peracetic acid is has been injected (about 150 mL). The sample is then washed. The total peracetic acid charged is 0.68 g (PAA)/g (wood).

Results

[159] Experiments prove that the method for producing holocellulose fibers according to the present disclosure is efficient and the consumption of organic peroxide, in this case PAA, can be reduced.

[160] Two-step treatment with organic peroxide, which may be peracetic acid, with an intermediate alkaline step refers to improving the efficiency of peracetic acid during delignification by removing some of the dissolved lignin and through solubility under partially oxidized lignin alkalines. The removal of these two lignin fractions leads to a decrease in the need for peracetic acid to obtain a certain degree of lignin removal, as illustrated in Figure 27, in which the consumption of PAA from the reference, from the pulps SD.BV.05B and SD .BV.12 was compared. Figure 27 illustrates the consumption of peracetic acid per gram of wood given in arbitrary units in the method comprising the addition of PAA in two steps with an intermediate alkaline step. On the left the reference, in the middle exactly the same experiment with continuous injection (SD.BV.05B), on the right an experiment with continuous injection at a lower temperature (SD.BV.12). A reduction of 20% and 28%, respectively, was obtained.

[161] In Figure 28, the consumption of peracetic acid per gram of wood is given in arbitrary units in the method comprising the continuous addition of PAA. On the left the reference, in the middle the same experiment with continuous injection (SD.BV.06), on the right an experiment with continuous injection at a lower temperature (SD.BV.07). A reduction of 28% and 45%, respectively, was obtained.

[162] Thus, the theory of chemical kinetics is in agreement with the findings of these experiments. Additionally, the pulp prepared by continuous injection of peracetic acid showed properties similar to those observed for pulps treated under conditions involving the use of peracetic acid (PAA) in the amount of 2.5 g PAA/g of fibers.

[163] Additionally, it was noted that the alkaline treatment allows the control of the cellulose ultrastructure. Alkaline extraction seems to be able to strongly modify the ultrastructure of cellulose, directly affecting the size of the cellulose fibril aggregates (LFAD: Dimension of the lateral fibril aggregate), without changing either the chemical composition (carbohydrate analysis) or the mechanical properties. (presented in papermaking). However, the control of this parameter is not fully mastered, but the alkaline stage seems to play a key role in this change.

[164] Figure 29 illustrates the chemical composition of samples SD.BV.05b (illustrating alkaline treatment without pH control and separating 2 stages of PAA), SD.BV.12 (illustrating the same concept with pH control) and SD.BV.16 (reference). SD.BV.16 was obtained with several consecutive stages of conventional peracetic acid. SD.BV.05b was obtained after a conventional treatment with peracetic acid, followed by an alkaline treatment (starting pH 12, room temperature, 1h), followed by another treatment with peracetic acid. The main change between SD.BV.16 and SD.BV.05b is the extraction stage added in SD.BV.05b. This change also resulted in a lower total consumption of peracetic acid (see Figure 27).

[165] Table 4 below shows the measured values for the different pulps. The reference samples give LFAD values of about 20 nm, when a pulp treated with this invention gives a value of 30.9 nm. This value is extremely important, since the development of mechanical properties on a macroscale is currently related to the size of the cellulose fibril aggregate. SD.BV.16 is the reference, SD.BV.05b is the one with unusual LFAD.

Table 4 Size Process “Radius- LFAD Load Load LFD LFAD FSP WRV X Ratio Mean WRV” (%) ssa total surface (nm) (nm) (g/g) (g/g) pore (2t) (surface/total ) Cry Cooking (m2/g) [µeq/g] [µeq/g] (nm) SD.BV.16 3.2 20.8 41% 128 1.88 2.00 29.3 255 45 18% SD. BV.5b 3.1 30.9 40% 86 1.35 1.88 31.3 212 65 31% SD.BV.7 3.1 20.2 40% 132 1.74 -- -- -- SD. BV.14 3.2 18.0 42% 148 2.12 1.76 28.7 218 28 13% 4.0 122 23.3 Kraft at 21 1.42 1.49 48 3 6.25% 5.2

[166] Figure 30 illustrates drainage time in a sheet former as a function of the increase in the tensile strength index in (kNm/kg) and as a function of the increase in the amount of holocellulose fibers in the pulp. It can be seen that using the holocellulose fibers obtained by the present production method in which less PAA is used than in the known methods, the strength was substantially increased while the drainage time was not substantially increased. It should be noted that the SD reference is a commercial pulp not containing holocellulosic fibers.

[167] The above description and examples are provided to further illustrate the features and advantages of the present invention. However, the scope of the invention is defined by the appended claims.

Claims (27)

1. Method for producing holocellulose fibers usable in a process for the production of paper by treating wood-based raw material with an organic peroxide, such as peracetic acid (PAA), characterized in that it comprises: i. continuously loading the organic peroxide into the wood-based raw material during treatment; and/or ii. loading the organic peroxide to the wood-based feedstock in at least two separate steps with an intermediate alkaline treatment step. 2. Method according to claim 1, characterized in that the intermediate alkaline treatment step is performed at a pH of 8 or more, or from pH 10 to 12, at a temperature of 15 to 100°C at atmospheric pressure and for a duration of at least 1 hour. 3. Method according to claim 1 or 2, characterized in that in at least one of at least two separate organic peroxide treatment steps, the organic peroxide is loaded in batches or continuously into the wood-based raw material during treatment. 4. Method according to any one of claims 1 to 3, characterized in that the treatment with organic peroxide is carried out at a temperature of 40 to 90°C or 55 to 75°C. 5. Method according to any one of claims 1 to 4, characterized in that the treatment with organic peroxide is performed at a pH of 2.5 to 5 or 4.0 to 4.8. 6. Method according to any one of claims 1 to 5, characterized in that continuous loading is performed at one or more load rates throughout the treatment. 7. Method for producing a strength agent for paper usable in a process for the production of paper, characterized in that it comprises producing holocellulose fibers by the method defined in any one of claims 1 to 6, optionally carrying out microfibrillation of the fibers of holocellulose to provide holocellulose nanofibrils (CNF), dry the holocellulose fibers or holocellulose nanofibrils, and break up the dried holocellulose fibers or holocellulose nanofibrils. 8. Process for the production of paper, characterized by the fact that it comprises the steps of: a. preparing a papermaking pulp comprising an aqueous pulp slurry comprising cellulosic fibers and having a fiber consistency of from 0.1 to 40% by weight, wherein the cellulosic fibers comprise or consist of wood-based holocellulose fibers and in that the amount of wood-based holocellulose fibers is from 0.5 to 100% by weight, based on the total weight of the cellulosic fibers, b. supply the paste to a yarn and form a web, c. emptying the web, and d. dry the web. 9. Process according to claim 8, characterized in that wood-based holocellulose fibers are produced by treating a wood-based raw material with an organic peroxide, preferably peracetic acid (PAA). 10. Process according to claim 8 or 9, characterized in that the holocellulose fibers are produced by the method defined in any one of claims 1 to 6. Process according to any one of claims 8 to 10, characterized in that the wood-based raw material for the holocellulose fibers comprises hardwood and/or softwood material. 12. Process according to any one of claims 8 to 11, characterized in that the holocellulose fibers are added after a refining step in step a) of sludge preparation. Process according to any one of claims 8 to 12, characterized in that step a) of preparing the pulp for papermaking comprises a step of adding an additive to the aqueous sludge, beating and/or refining the aqueous slurry. . 14. Process according to claim 13, characterized in that the additive comprises holocellulose fibers which are added in an amount of 0.5 to 80% by weight, or from 2 to 60% by weight or from 4 to 4 55% by weight, based on the dry weight of the cellulosic fibers. 15. Process according to claim 13 or 14, characterized in that the additive comprises a dry strength agent chosen from nanocellulosic materials, loaded and unloaded starch, gum derivatives, synthetic copolymers with acrylamide and combinations thereof . 16. Process according to any one of claims 13 to 15, characterized in that the additive comprises a cationic starch. 17. Process according to claim 16, characterized in that the cationic starch is added in an amount of 0.5 to 5% by weight, based on the dry weight of the cellulosic fibers. 18. Process according to any one of claims 13 to 17, characterized in that the additive comprises a holocellulose CNF. 19. Process according to claim 18, characterized in that the holocellulose CNF is added in an amount of 0.1 to 10% by weight, or from 0.5 to 5% by weight, based on dry weight of the folder. Process according to any one of claims 13 to 19, characterized in that the additive comprises a wet strength agent, which is a resin chosen from urea-formaldehyde resins, melamine-formaldehyde resins, polyamide-amine-epichlorohydrin resins and combinations thereof. 21. Process according to any one of claims 13 to 20, characterized in that the additive comprises a retention aid chosen from loaded or unloaded polyacrylamide (PAM), polyethyleneimine (PEI), colloidal silica (CS), bentonite and combinations thereof. 22. Process according to any one of claims 13 to 21, characterized in that the additive is cationic polyacrylamide (CPAM). 23. Process according to any one of claims 8 to 22, characterized in that the cellulosic fibers comprise fibers from a kraft pulp, soda pulp, sulfite pulp, mechanical pulp, thermomechanical pulp, semi-chemical pulp or chymo to thermomechanical pulp, recycled or mixtures thereof in an amount from 0 to 99.5% by weight, based on the total weight of the cellulosic fibers. 24. Paper, characterized in that it is obtained by the process defined in any of claims 8 to 23. 25. Use of paper defined in claim 24, characterized in that it is used as packaging material. 26. Use of the paper defined in claim 24, characterized in that it is like a corrugated fiber board. 27. Use of wood-based holocellulose fibers, of holocellulose fibers produced by treating a wood-based raw material with an organic peroxide, characterized in that it is in a process that comprises a delignification and a washing step, in a papermaking process to improve paper strength.